ALMA observations of water deuteration: a physical diagnostic of the formation of protostars
Artikel i vetenskaplig tidskrift, 2019
Aims. The aim is to determine the HDO/H20 ratio in the inner warm gas toward three low-mass Class 0 protostars selected to be in isolated cores, i.e., not associated with any cloud complexes. Previous sources for which the HDO/H20 ratio have been established were all part of larger star-forming complexes. Determining the HDO/H20 ratio toward three isolated protostars allows comparison of the water chemistry in isolated and clustered regions to determine the influence of local cloud environment.
Methods. We present ALMA Band 6 observations of the HDO 31,2-22,1 and 21,1-21,2 transitions at 225.897 GHz and 241.562 GHz along with the first ALMA Band 5 observations of the H2180 31,3-22,0 transition at 203.407 GHz. The high angular resolution observations (0'.'3-1'.'3) allow the study of the inner warm envelope gas. Model-independent estimates for the HDO/H20 ratios are obtained and compared with previous determinations of the HDO/H20 ratio in the warm gas toward low-mass protostars.
Results. We successfully detect the targeted water transitions toward the three sources with signal-to-noise ratio (S/N) > 5. We determine the HDO/H20 ratio toward L483, B335 and BHR71 IRS1 to be (2.2 0.4) x 10-3, (1.7 0.3) x 10-3, and (1.8 0.4) x 10-3, respectively, assuming Tex = 124 K. The degree of water deuteration of these isolated protostars are a factor of 2-4 higher relative to Class 0 protostars that are members of known nearby clustered star-forming regions.
Conclusions. The results indicate that the water deuterium fractionation is influenced by the local cloud environment. This effect can be explained by variations in either collapse timescales or temperatures, which depends on local cloud dynamics and could provide a new method to decipher the history of young stars.
ISM: individual objects: B335
astrochemistry stars: formation
ISM: individual objects: BHR71-IRS1
ISM: individual objects: L483
S. S. Jensen
J. K. Jorgensen
University of Tsukuba
Université de Bordeaux
E. F. van Dishoeck
Magnus V. Persson
Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)Vol. 631 A25
Astronomi, astrofysik och kosmologi